package dem1;

import java.util.Arrays;

public class PriorityQueue {
    public int[] elem;
    public int usedSize;

    public PriorityQueue() {
        elem = new int[10];
    }

    /**
     * 建堆的时间复杂度：
     *
     * @param array
     */
    public void createHeap(int[] array) {
        if (array.length > elem.length){
            elem = Arrays.copyOf(array,2 * elem.length);
        }
        for (int i = 0; i < array.length; i++) {
            elem[i] = array[i];
            usedSize++;
        }
        for (int i = (usedSize - 2) / 2; i >= 0 ; i--) {
            shiftDown(i,usedSize);
        }
    }

    /**
     *
     * @param root 是每棵子树的根节点的下标
     * @param len  是每棵子树调整结束的结束条件
     * 向下调整的时间复杂度：O(logn)
     */
    private void shiftDown(int root,int len) {
        int child = root * 2 + 1;
        while (child < len) {
            if (child + 1 < len && elem[child] < elem[child + 1]) {
                child = child + 1;
            }
            if (elem[child] > elem[root]) {
                int tmp = elem[child];
                elem[child] = elem[root];
                elem[root] = tmp;
                root = child;
                child = root * 2 + 1;
            }
        }
    }

    /**
     * 入队：仍然要保持是大根堆
     * @param val
     */
    public void push(int val) {
        if (isFull()){
            elem = Arrays.copyOf(elem,2 * elem.length);
        }
        elem[usedSize] = val;
        usedSize++;
        shiftUp(usedSize - 1);
    }

    private void shiftUp(int child) {
        int parant = (child - 1) / 2;
        while (child > 0){
            if (elem[parant] < elem[child]){
                int tmp = elem[parant];
                elem[parant] = elem[child];
                elem[child] = tmp;
                child = parant;
                parant = (child - 1) / 2;
            }else {
                break;
            }
        }
    }

    public boolean isFull() {
        return usedSize == elem.length;
    }

    /**
     * 出队【删除】：每次删除的都是优先级高的元素
     * 仍然要保持是大根堆
     */
    public void pollHeap() {
        elem[0] = elem[usedSize - 1];
        usedSize--;
        shiftDown(0,usedSize);
    }

    public boolean isEmpty() {
        return usedSize == 0;
    }

    /**
     * 获取堆顶元素
     * @return
     */
    public int peekHeap() {
        return elem[0];
    }
}